1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a method of updating a list of digital control channels (DCCHs) in a mobile station, thereby enabling the rapid acquisition of a digital control channel.
2. Description of Related Art
Existing digital radio telecommunications networks operating under standards such as IS-136 utilize a digital control channel (DCCH) to pass control information to and from mobile stations operating within the service areas of the networks. A DCCH may be deployed in a cell on any frequency in the cellular or Personal Communication Services (PCS) frequency bands. Current techniques for acquiring a DCCH are based on proprietary mobile station techniques utilizing certain tools provided by IS-136. However, because of the wide range of frequency options, it is often difficult for a mobile station to rapidly acquire an available DCCH.
Analog control channels (ACCs) are easier to locate because they are located on a few consecutive dedicated frequencies. In addition, under IS-136, the ACCs broadcast a DCCH pointer. Therefore, one of the more commonly utilized techniques to locate an available DCCH is to first find an ACC, and then look for the broadcast DCCH pointer. This technique, however, is useless for 1900-MHz PCS frequency band operation since there is no ACC in the PCS frequency band. Furthermore, many mobile stations are digital-capable only, and this technique is useless for those mobile stations because they do not have the capability to decode and read an ACC. In addition, some 800-MHz cellular networks are digital only. Therefore, the technique of finding an ACC and utilizing the DCCH pointer does not work in these networks either.
Another technique for acquiring a DCCH is for the mobile station to scan a history list of DCCHs. This list is usually short, and therefore, does not normally take excessive time to scan. This technique may be ineffective, however, if the serving DCCH is not in the mobile station's history list. This may occur if the mobile station is powered up in a cell in which it has not operated before, or if the mobile station has operated there before, but the serving DCCH is no longer on the list due to the limited size of the list and the number of DCCHs subsequently utilized. In addition, a cell's DCCH frequency plan may be modified by an operator or by closed-loop adaptive channel allocation (ACA). In this case, the DCCH history list built up prior to the DCCH frequency plan modification becomes obsolete.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 5,404,355 to Raith (Raith) and PCT Patent Application WO95/12936 to Henry et al. (Henry) discuss subject matter that bears some relation to matters discussed herein. Raith discloses a method of transmitting information on a DCCH between a base station and a mobile station in a cellular telecommunication system. The information is sent as a plurality of information elements, and a change flag is transmitted to indicate whether the value of any of the information elements has changed. Raith, however, does not teach or suggest a method of rapidly acquiring a DCCH in a cellular/PCS system.
Henry discloses a method and system for locating control channels, particularly digital control channels. The channels which are likely to be assigned as a DCCH are grouped, and a mobile station searching for a control channel begins its search with this group. Other channels currently serving as digital traffic channels (DTCs) contain a field in which a pointer redirects a searching mobile station to the DCCH. In addition, information describing the location of a control channel is also placed in call release messages so that the mobile station does not have to relocate a new control channel following handoff to a new base station. However, the system and method of Henry have disadvantages when a mobile station operates in a cellular/PCS network because of the wide range of frequency options. Since a DCCH may be deployed in a cell on any frequency in the cellular or PCS frequency bands, it is often difficult for a mobile station to rapidly acquire an available DCCH.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of updating a list of DCCHs in a mobile station thereby enabling the rapid acquisition of a DCCH in a cellular/PCS system in which the DCCH may be deployed on any frequency in the cellular or PCS frequency bands. The present invention provides such a method.